Hey Bear, you should try BB's improved LED park/tail/stop/turn light fix.  Uses a combo of 1157 LED bulbs, two incandescent 1157 bulbs, a stone stock bi-metal flasher (available anywhere), and makes the tail/stop/turns very visible.  Oh...and it's a whole bunch cheaper than buying special electronic do-dads.

BB-1

BB,  can you post a link to your improved LED park/tail/stop/turn light fix?

I am using a resistor in series with my taillight LEDs.  Everything works as normal and no special flashers needed.

John Ha wrote:

Motorcycles have this same issue but many have a dedicated "module" to control the lighting so replacing just a flasher isn't an option.  They use resistors instead - there are tons of kits with resistors out there to fix the problem.  I believe, though, that the resistors have to be in parallel with the LEDs, not in series.

Thanks, John.  Went to bed thinking about MS's comment.  Those RX need to cause an increase in current flow, not drop voltage.  I get the same effect by using one incandescent bulb in parallel with the LEDs.  I do have to have diode on each side to stop the turn sigs from flashing both sides.

BB-1

The benefit of led’s is cool operation and low current draw that is why they need a special flasher, a resistor in series defeats the purpose, touch it, it gets hot.
The resistor in series makes the led draw the same current as an incandescent bulb so a regular flasher module will work.
A led flasher usually has a pigtail ground wire.

MS wrote:

I'm no electrical engineer, but doesn't current take the path of least resistance?  That said, in parallel, it seems like the least amount of current to light the bulb would just pass through the bulb, and the resistor would just get ignored in the circuit?  I am probably wrong, but please 'splan it to me, Lucy.

The two kits I bought at OReilly are wired in series, as I recall.  Whatever the case, they resulted in everything working properly.

LEDs do need a series resistance to work in a 12 V system since a typical LED only requires 2-3 V and a few milliamps to illuminate.  There is a need to have the series resistance to function as a voltage divider.  

However, the issue with the flasher not working right is that there is too little current.  So you need a way to increase the current through the circuit to a value equivalent to what a bulb draws.  

Remember Ohm's Law:  Voltage = Current x Resistance or, restated, Current = Voltage/Resistance.  

To increase current for a constant voltage input, you need to reduce the total resistance of the circuit.  Adding a resistor in series increases the circuit resistance while adding a parallel resistor decreases the total resistance - in a parallel resistance circuit, the total resistance is calculated using (R1 x R2)/(R1+R2).  I leave the math to the reader :-)

Bullet Bob wrote:

Rudi wrote:

T
The resistor in series makes the led draw the same current as an incandescent bulb so a regular flasher module will work.

Rudi, did you mean "resistor in parallel" here?

MS:  The LEDs have a very high resistance, hence, they don't pass enough current (.1 amp or so) through the bi-metal flasher to make it operate.  The added parallel resistor of say 20 ohms or so will pass something over a half amp when connected from the hot wire to ground.  That's enough to heat the bi-metal  flasher.  But, you are getting nothing but heat for the wasted current flow.  If you use an incandescent bulb to provide the needed flasher current, you at least get the light for the added current draw.
If the RX is connected in series with the LEDs it really does nothing since it only passes the current that's required by the downstream load...the LEDs.

 
No I meant series.
If you put a resistor  in parallel with a led, the combination will have less resistance  than the lowest component.

First thing I ALWAYS do with my blinkers is.................check-the-fluid-level!   Saves a lotta time and heartache.
6sally6

Thanks Rudi and Bearcat

This makes sense. My resistors require same current as incandescent bulbs to operate an LED.  i will consider swapping the flashers and eliminating the resistors.  I want to add LED front turn signals and backup lights as well. So, buying two flashers should be just as cost effective as four resistors.

Steve, check out Gary's daytime running lights/indicator combo, and his 700 lumen reverse lights. Dearer than most, but the best stuff you can get IMHO. And a nice guy.
https://vintageleds.com/1964-1966

My car has an extra flasher for the emergency flasher circuit.

I believe the three prong flasher provides output for a single turn signal dash light. 
BB